Deadlocking States in Context-Free Process Algebra

Recently the class of BPA (or context-free) processes has been intensively studied and bisimilarity and regularity appeared to be decidable (see [CHS95, BCS95, BCS96]). We extend these processes with a deadlocking state into BPAδ systems. Bosscher has proved that bisimilarity and regularity remain decidable [Bos97]. We generalise his approach introducing strict and nonstrict version of bisimilarity. We show that the BPAδ class is more expressive w.r.t. (both strict and nonstrict) bisimilarity but it remains language equivalent to BPA. Finally we give a characterization of those BPAδ processes which can be equivalently (up to bisimilarity) described within the ‘pure’ BPA syntax.